Various endovascular devices, including without limit central venous catheters (“CVC”), may be inserted into the vasculature of a patient to detect and/or treat various health issues. CVCs are endovascular devices including any catheter designed to utilize the central veins (e.g., subclavian and superior vena cava) or right sided cardiac chambers for the delivery and/or withdrawal of blood, blood products, therapeutic agents, and/or diagnostic agents. CVCs also include catheters inserted into the central veins or right sided cardiac chambers for the acquisition of hemodynamic data. Standard central venous catheters for intravenous access, dialysis catheters, percutaneously introduced central catheters (“PICC” lines), and right heart (“Swan-Ganz™”) catheters are examples of CVCs. In some applications, an endovascular device, e.g., a central venous catheter (CVC), may be inserted into the superior vena cava (SVC) of a patient.
The specific location placement of an endovascular device is very important and can have a significant impact on the health of the patient. For example, a central venous catheter (CVC) with its tip located in the ideal position provides reliable vascular access with optimal therapeutic delivery, while minimizing short and long-term complications. In the United States, the ideal catheter tip placement of a CVC in the SVC is within 10 mm from the junction of the SVC and the right atrium (i.e., the “cavoatrial junction”). According to FDA, the tip of catheter should not be placed in, or allowed to enter, the right atrium of the heart. In 1989, the Food and Drug Administration issued a warning citing an increased risk of perforation of the right atrium, clot formation, and arrhythmias among other potential complications resulting from the tip of the CVC being placed inside the right atrium.
While CVCs have been used for many years, determining the position of the tip of the CVC has always been problematic. Further, in addition to the need to know where the tip is during initial placement, the CVC may migrate or otherwise move after the initial placement and require re-positioning. Therefore, the operator must monitor or periodically reevaluate the location of the tip.
Electrocardiogram (ECG) based guidance can be used as a positioning technique for catheter tip placement and confirmation. The electrical conduction system of the heart creates specific electrical signals, electrical energy distributions and behaviors thereof which are indicative of specific locations in the thoracic cavity and/or of specific heart functions or conditions. When measured endovascularly or intravascularly, i.e., from within blood vessels or from within the heart, certain parameters of the electrical activity of the heart can be used to identify specific locations in the cardiovascular system and/or functional conditions, normal or abnormal. An electrocardiogram (ECG) measures electrical potential changes occurring in the heart. The P wave portion of the ECG waveforms represents atrial muscle depolarization: the first half is attributable to the right atrium and the second half to the left atrium. Under normal circumstances, atrial muscle depolarization is initiated by a release of an excitatory signal from the sino-atrial node, a specialized strip of tissue located at the juncture of the superior vena cava (“SVC”) and right atrium.
Some methods of ECG based guidance employ morphological and/or spectral analysis of ECG waveforms, specifically P waves, to position a catheter tip. (See Patent Application Publication US2010/0317981, which is incorporated by reference in its entirety into this application). Techniques of using ECG waveforms to locate the tip of a CVC have shown that both the magnitude and shape of the P wave changes depending upon the positioning or location of the electrode attached to the tip of the CVC. Normally as the electrode attached to the tip of the CVC moves from the SVC toward the sino-atrial node, the maximum value of the absolute value of the voltage of the P wave increases.
However, placement or location methods using P wave or other ECG waveform analysis have many disadvantages. For example, it is difficult to detect the exact location of the tip within last one-third of the SVC before the cavoatrial junction using this method. Accordingly, the final fixed position of the tip is not always optimal. Further, to identify the proper tip position, one must identify the point where the P wave is tallest; however, to identify the tallest P wave clinicians generally must “cross-the-line” by briefly entering the atrium (i.e., they must move beyond the point where the P wave is tallest to know where the tallest point is). This entry into the atrium is contrary to FDA regulations and causes additional and unnecessary risks for the patient. Also, successful placement of the CVC using this method ends up depending a great deal on the experience of the clinician, and is more difficult for less experienced clinicians. Another disadvantage of methods focused on analyzing P waves or other waveforms is that heart abnormalities, arrhythmias, anatomic variability, noise and artifacts may affect detection and interpretation of P-waves morphological changes.
Disclosed herein are new methods of objective assessment of the location of the catheter tip by analyzing ECG data point to point variability, which avoids the above disadvantages. The method evaluates the complexity of changes of an ECG signal to calculate the distance from the catheter tip to the cavoatrial junction. The method is based on chaos theory and the concept of self-organized criticality (SOC). Systems at critical transition point between chaos and order are said to be in a state of self-organized criticality. The concept of SOC may be applied in different areas such as biological systems, statistics, nature, and large electronic circuits.